Issue 66

G.V. Krishna Reddy et alii, Frattura ed Integrità Strutturale, 66(2023) 261-272; DOI: 10.3221/IGF-ESIS.66.16

the composites did not improve with an increase in the weight fraction of SiC particles, while the addition of graphite negatively impacted the absorption capacity. K EYWORDS . Metal matrix composite, Al-graphite composite, Impact energy, Al-SiC, Post-ageing cooling.

I NTRODUCTION

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l6061 and its composites are widely used in various applications that require high strength and impact resistance, such as aerospace, automotive, and structural engineering [1]. Zakaria Belabed et al. [2–4] used some advanced micromechanical models to evaluate composites' mechanical properties. The mechanical properties of Al6061 and its composites can be improved by heat treatment processes such as ageing. Consequently, the precipitation of reinforcing phases occurs within the aluminium matrix [5]. However, the cooling method applied post-ageing treatment can also influence these materials' impact on energy absorption capacity. The cooling rate can directly affect the material's microstructure and various mechanical properties [6], including the impact energy absorption capacity. The cooling rate can significantly affect the microstructure and properties of aluminium alloys [7,8]. During the cooling process, the speed at which a material's temperature decreases influences the transformation of its microstructure, ultimately shaping its mechanical and physical characteristics [9]. Rapid cooling rates, such as water or oil quenching [10], can enhance mechanical properties by producing a fine-grained structure [11]. This results in increased mechanical strength, hardness, and improved wear resistance. The finer grains also inhibit the growth of large intermetallic particles, which can be detrimental to material properties. However, they also pose challenges such as potential distortion, cracking, or even complete failure due to residual stresses [12,13]. Conversely, slower cooling rates, like those associated with controlled furnace cooling, permit the growth of coarser microstructure (larger grains) due to the extended time available for atomic diffusion [14]. This can improve ductility, better formability, and enhanced resistance to stress corrosion cracking. However, it may also result in reduced strength [15]. Moreover, the cooling rate influences the precipitation kinetics of various alloying elements. Rapid cooling can sometimes trap solute atoms within the lattice structure, hindering the formation of certain precipitates. On the other hand, slower cooling rates allow for more controlled precipitation, contributing to improved age-hardening characteristics. The appropriate cooling rate depends on the specific alloy and the desired properties for the application [16]. In industrial practices, various post-ageing cooling methods are frequently utilised for aluminium alloys, and each process imparts unique impacts on material properties. These techniques encompass furnace cooling, characterised by controlled cooling in a controlled environment; air cooling, permitting materials to cool in the surrounding air naturally; and water quenching, involving rapid cooling through immersion in water or oil [17]. However, the effect of these cooling methods on the impact energy absorption capacity of Al6061 and its composites is not well understood. Therefore, there is a need to investigate the effect of post-ageing cooling methods on the impact energy absorption capacity of Al6061 and its composites. The study's innovation arises through its emphasis on investigating the impact energy absorption capacity of Al6061 and its composites, particularly in terms of various post-ageing cooling (PAC) techniques. While the mechanical properties of these composites have been studied extensively regarding heat treatment and ageing, the role of cooling methods after the ageing process has not been well-explored. By conducting a systematic investigation on the impact energy absorption capacity of Al6061 and its composites under different cooling conditions (furnace cooling, air cooling, and water cooling), this study aims to fill the knowledge gap and provide insights into the effect of cooling methods on the final mechanical performance of the materials.

M ATERIALS AND METHODS

Materials he materials used in this study were Al6061 alloy, graphite particles, and SiC particles, as shown in Fig.1. The Al6061 alloy was selected as the matrix material due to its high strength, good machinability, and widespread use in various industries [18]. The graphite and SiC particles [19] were chosen as the reinforcement materials due to their high

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